(1) Field of the Invention
The present invention relates to a separating device, in particular, relating to a separating device for separating a sheet-like medium stuck on the outer periphery of a photoreceptor drum by means of a separating member.
(2) Description of the Prior Art
Conventionally, in image forming apparatus using electrophotography such as a facsimile machines, printers and the like, image output is carried out by the steps of electrifying a rotationally driven photoreceptor drum by a charger, forming an electrostatic latent image on the photoreceptor drum by irradiation with light in accordance with image information, forming a toner image by applying toner to this electrostatic latent image by means of a developing device and transferring the toner image onto a recording medium such as a sheet medium, paper or the like.
Of such image forming apparatus, there has been known a configuration that includes a separating device for separating the recording medium from the photoreceptor drum by force by bringing a separating member into sliding contact with the photoreceptor drum, in order to prevent the recording medium to which the toner image formed on the photoreceptor drum has been transferred, from remaining electrostatically stuck to the photoreceptor drum.
Next, one example of such a conventional separating device will be described with reference to the drawing.
FIG. 8A is an illustrative diagram showing a state in which a paper separation claw of a conventional separating device is abutting the photoreceptor drum when the claw has been worn down. FIG. 8B is a detailed diagram of the H portion illustrated in FIG. 8A.
As the prior art example of a separating device in an image forming apparatus, in order to forcibly separate the paper (recording medium) from a photoreceptor drum 3, the image forming apparatus is provided with a separating device that is constructed so that a paper separation claw (separating member) 131 of a tapered wedge-shape is applied onto photoreceptor drum 3 with a fixed load so as to mechanically separate the paper attracted to the photoreceptor drum 103 surface as shown in FIG. 8A.
As shown in FIG. 8A, this paper separation claw 131 is pivotally supported by a supporting shaft 132 as a rotational supporting point and urged in the direction of an arrow SP by means of an unillustrated spring member so that the front end 131a of paper separation claw 131 abuts against the photoreceptor drum 103 surface with a load as low as 1 g by taking damage to photoreceptor drum 103 into consideration.
Since photoreceptor drum 3 rotates while paper separation claw 131 is being abutted thereagainst, the abutment, designated at 131b in the front end 131a of paper separation claw 131 becomes worn down with increase in rotating time (the number of sheets) of photoreceptor drum 3, as shown in FIGS. 8A and 8B. If this wearing progresses rapidly, it is impossible to extend the maintenance cycle of the image forming apparatus since the life of paper separation claw 131 is estimated to be short.
Further, when a material having an extremely high wear resistance is used in order to suppress paper separation claw 131 from being worn, this scratches or damages photoreceptor drum 3, causing the problem of shortening the life of photoreceptor drum 103.
Further, as front end 131a of paper separation claw 131 is worn down, the front end 131a of paper separation claw 131 floats from the photoreceptor drum 103 surface due to a slight eccentricity of photoreceptor drum 3 as the photoreceptor rotates, causing the problem that the required paper separating performance cannot be obtained. That is, if the paper could not be separated from photoreceptor 103 by paper separation claw 131, paper jamming takes place inside the apparatus.
To deal with this, patent document 1 (Japanese Patent Application Laid-open H11-219035) proposes a separating device built in an image forming apparatus in which, as the means of claw-like separating member to be abutted against the photoreceptor drum, the surface of the claw opposing the photoreceptor drum is formed so as to allow the leftover toner on the photoreceptor drum surface to pass therethrough without blocking. This configuration enables the separating device to prevent damage to the photoreceptor drum surface due to local abrasion of the front end part of the claw-like separating member.
On the other hand, patent document 2 (Japanese Patent Application Laid-open 2009-265292) proposes a technology in which the rotational supporting point of the separating member is changed from the photoreceptor in a radial direction of the photoreceptor drum in order to prevent the front end of the separating member that should abut the photoreceptor drum from floating due to eccentricity of the photoreceptor drum during rotation to secure stable separation performance of the separating member, suppress foreign substances from building up between the photoreceptor drum and the separating member and suppress abrasion on the photoreceptor surface.
However, since, in the configuration shown in patent document 1, the position of the rotational axis that enables the claw-like separating member to pivot is fixed, the front end part of the claw-like separating member is abraded so that the contact area of the claw-like separating member with the photoreceptor drum becomes greater, causing the problem that the front end part (the tip of the contact surface) of the claw-like separating member floats due to eccentricity of the photoreceptor drum, resulting in separation failure. Further, as the contact area between the claw-like separating member and the photoreceptor drum becomes greater, the risk of foreign substances building up between the claw-like separating member and the photoreceptor drum becomes higher, giving rise to a problem that the foreign substances accelerate abrasion of the photoreceptor drum.
In the configuration of patent document 2, though it is possible to secure stable separation performance over a long period and achieve long lives of the separating member and photoreceptor drum, it is necessary to provide a mechanism or other means for changing the position of the rotational supporting point of the separation claw. Further, no consideration is given about the influence of the reactive force the separating member receives from the photoreceptor drum and the rotational moment generated in the separating member, resulting from the enlargement and complexity of the arrangement around the separating member, hence there occurs the problem that the front end of the separating member abutting against the photoreceptor drum floats.